AMP-activated protein kinase (AMPK) activation increases fatty acid oxidation in skeletal muscle by decreasing malonyl CoA concentrations. However, this may not explain the long-term effects of AMPK activation. Here we show that AMPK activation by 5-amino-imidazole-4-carboxamide ribonucleoside (AICAR) increases mRNA expression of PPAR alpha target genes and PGC-1 in cultured muscle cells and mouse skeletal muscle, and that inhibition of PPAR alpha and PGC-1 by siRNAs prevents AICAR-stimulated increase in fatty acid oxidation. These data suggest that a novel transcriptional regulatory mechanism involving PPAR alpha and PGC-1 exists that is responsible for long-term stimulation of fatty acid oxidation in skeletal muscle by AICAR. (c) 2005 Elsevier Inc. All rights reserved.